Low voltage problem

Make certain VR is grounded. "Work" VR connector in/ out several times to 'scrub' terminals and "feel" for tightness. Remove connector check if you have power (key in run) to BOTH terminals with all other wiring connected normal.

The blue gets battery power from the key
The green is fed back power from the blue to one field---through the field--and back to the VR on the green

You can double check field wiring is OK by jumpering across VR terminals, then removing blue wire at alternator and grounding that terminal as you did the green. If it charges, wiring is likely OK

Replace VR

These do not fail often